WASHINGTON  Federal lawmakers Wednesday criticized the U.S. Environmental Protection Agency for not moving faster to determine whether "intersex" fish in the Potomac River and its tributaries signal the presence of pollutants that might be harmful to humans.

At a House Government Reform Committee hearing, lawmakers and environmental groups expressed alarm at a survey last year by the U.S. Geological Survey that found an unusually high number of male smallmouth and largemouth bass with female sexual characteristics.

They also worried that the presence of egg-bearing males at locations in Washington, Maryland and Virginia could be a sign that something is dangerously amiss.

"Fish are like canaries in the coal mine," said Rep. Chris Van Hollen, D-Md.

It is not clear what is causing the changes, though a combination of chemical pollutants is suspected. The reaction could be triggered by estrogen from birth control pills and human waste that makes its way into the waterways from sewage treatment plants, or manmade chemicals in pesticides and cosmetics.

Pollutants that interfere with the hormones of myriad animals have been a concern for about 10 years. Intersex fish were first discovered in the Potomac rivershed in 2003, about 200 miles upstream from Washington.

Since 1996, the EPA has been trying to develop a screening program to identify these so-called "endocrine disruptors" that are confusing the fish's reproductive systems. But the agency says the science has proven to be complicated and research is still ongoing.

Rep. Jim Moran, D-Va., said that taking 10 years was entirely too long. "It seems (the EPA) looks for any excuse it can find to delay the implementation of regulations that could affect the public's health," he said.

Benjamin Grumbles, the EPA's assistant administrator for water, said the first tests were expected by the end of next year. He told lawmakers the issue was particularly challenging because of the difficulty of determining how various compounds interact.

"We don't have a lot of information," Grumbles said.

In the meantime, lawmakers pressed federal scientists for reassurances that it was safe to drink the Potomac's water and eat its fish. Rep. Elijah Cummings, D-Md., said he was particularly concerned for pregnant women.

"I don't want us looking back 10 years from now saying we didn't move with the appropriate urgency," Cummings said.

He also pressed federal scientists to rate on a scale of 0 to 10 the seriousness of the issue. Grumbles replied he would give it an 8.

"Fish are warning signs and we need to take it seriously," Grumbles said.

Still, officials representing three of the Washington region's drinking-water utilities testified that they continue to meet federal drinking water standards and there's no evidence tap water is unsafe.

But Ed Merrifield, executive director of the environmental group Potomac Riverkeeper, wasn't satisfied.

"If scientists have not yet determined what pollutant is causing a reproductive health problem in fish in the Potomac, how can anyone say it is not in our drinking water?" he asked.